1. Field of the Invention
The present invention relates to a magnetic sheet, a wireless charging sheet, and a method for manufacturing a magnetic sheet, and more particularly, to a magnetic sheet that can reduce magnetic losses due to eddy currents, a wireless charging sheet, and a method for manufacturing a magnetic sheet.
2. Description of the Related Art
Wireless charging has a system in which a magnetic field induced by an AC current generates an induced electromotive force in a coil inserted in a wireless charging module and the induced electromotive force is charged in a secondary battery again. The wireless charging using electromagnetic induction consists of a power transmission coil, which transmits power, and a power receiving coil, which receives a magnetic field generated in the power transmission coil. At this time, when a metal object, for example, a battery approaches the power receiving coil, an eddy current is generated in the metal by a magnetic field generated in the power receiving coil, resulting in a reduction in efficiency due to heat and loss of magnetic field in the metal object. In order to prevent an eddy current loss in the metal object, a magnetic sheet is inserted between the power receiving coil and the metal object. At this time, characteristics required for the magnetic sheet are high saturation flux density and low loss in the frequency band used and particularly there is a trend toward slimming of the sheet by increasing magnetic characteristics of the sheet according to slimming of portable devices.
Currently, a ferrite sheet, which is obtained by performing sintering using ferrite, which is a ceramic magnetic material, as a raw material, and a metal-composite magnetic sheet, which is prepared by flaking metal magnetic powder of sendust and Fe—Si—Cr and mixing the metal magnetic powder with a polymer resin, have been mainly used as the magnetic sheet. Comparably, a metal foil or a metal magnetic sheet has been limitedly used since it has very high saturation flux density and magnetic loss in the wireless charging frequency band and thus deteriorates wireless charging efficiency.